Strain of Hansenulla californica yeast used for the decomposition of polychlorinated biphenyls

ABSTRACT

Hansenulla californica yeast strain VKPM Y-2284 is capable of degrading polychlorinated biphenyls (PCBs). The strain may be employed to detoxicate environment media and PCB-containing industrial wastes. To produce biomass, the strain is incubated on media which contain carbon sources, nitrogen sources and mineral salts. The strain is cultivated by a subsurface method up to a titer from 5.0.106 to 1.0x107 cells per cu cm. The produced biomass is employed for degrading PCBs in concentrations from 106 to 105 cells per cu cm. The strain ensures from 30 to 50% reduction in PCB content in soil and water.

This application is a 371 of PCT/RU98/00037 Feb. 13, 1998.

FIELD OF THE INVENTION

The present invention relates to biotechnology, ecology, environment protection, and particularly to bioremediation of environment media from polychlorinated biphenyls (PBCs), and provides a new yeast strain which is able to degrade PCBs under aerobic conditions in situ in environment media.

BACKGROUND OF THE INVENTION

Introduction of chemical advances into industry and household involves many hazards of immediate and long-term chemical impact. As of now, the issue of environment pollution control has become extremely pressing.

PCBs have been manufactured since 30th and found application for the most part in electrical industry. By late 60th, it has turned out that the environment contained from 300 to 500 thousand tons PCBs (Tarasov V.V. Contamination of the Environment with Polychlorinated Biphenyls and Ways for Minimizing Their Impact, Collection of Scientific Works of RKhTY LXXV Years/Main Scientific Achievements. Moscow, 1996, p.24-41). Annual release of PCBs averages 2000 tons. PCBs penetrate into the environment as the result of failures of PCB-containing equipment and systems and due to incineration. PCBs penetration into soil is caused by equipment failures or discharges of untreated industrial sewage from plants that employ PCBs in their production run, and by utilization of sludge from irrigated fields. Owing to a high absorption power and a low degradation ability, polychlorinated biphenyls accumulate in the soil surface layer at a depth of 2-10 cm and in bed sediments. PCBs have been detected substantially in all living nature. PCB is a polytropic poison which affects essentially all body organs and systems.

According to data published by the WHO, a human appears to be the most PCB-sensitive creature. PCBs relate to substances of the first hazard group.

Worldwide practice for remediating environment media from PCBs is to use in general various physical and chemical methods.

In Germany, PCB-contaminated soil is remediated by a method developed by National Research Council, Canada. According to the method, special dispersion sodium-oil blends are introduced into old landfill sites to assist in chlorine release from PCBs with formation of common salt. (see Deckwer W.-D. Weppen P. Review of Methods for Remediating Contaminated Soil and Refused Territories Contaminated with Hazardous Wastes.—Chemie-Ingenieur-Technik, 1987, Vol.59, #6, p.457-467). Gebruder Kemmer/Jng Buro Harbauer Group (Germany) has invented a method for decontamination of PCB-contaminated soil, which involves excavation of the soil. The method includes crushing and sieving the soil, the obtained fractions being separately decontaminated with water to which surfactants are added. Flush liquid is supplied to a sewage treatment plant (Schondorf T., Munz K. H. Removal of Polychlorinated Biphenyls from Contaminated Soil.—Chem.Rosch. (Schweiz.), 1988, v.41, #45, s.18).

Kloeckner Oecotec GmbH, Germany, has invented a method for remediation of PCB-contaminated soil, involving washing the soil under a high pressure at a pilot plant. The soil in the form of pieces of up to 10 mm in diameter is ground in a conical water jet. A high pressure of 250 bar in an annular pipe and a great rate of 200-250 m/s promote a complete homogenization and separation of smallest components and hazardous substances. After the water treatment of the soil, the suspension is separated by one of the following methods: precipitation, cyclone separation, centrifugation, filtration, etc. Developed in Russia are methods for soil decontamination from PCBs with the aid of a propulsion, plasmatrons (Tarasov V. V. Contamination of the Environment with Polychlorinated Biphenyls and Ways of Minimizing Their Impact. Collection of Scientific Works of RKhTY LXXV years/Main Scientific Achievements, Moscow, 1996, p.24-41).

All of the above methods suffer a number of essential problems: they are cumbersome, require great investments and disturb the soil ecological equilibrium. Since late 70th, an ever increasing interest has been expressed in bioremediation methods. It is well known that various bacterial strains and fungi are able to degrade PCBs. They include microorganisms of Pseudomonas genus (Pseudomonas putide for degrading polychlorinated biphenyls. U.S. Pat. No. 4,843,009, Int.C1. C12N 1/12, Application No.866501 filed on May 23, 1986) and fungi Whit Rod Funtigus. Phanerochaete chrysosporium (Degradation of 4′,4′-Dichlorobiphenyl, 3,Y,4,4′-Tetrachlorobiphenyl, and 2,2′,4,4′,5,5′-Hexachlorobiphenyl by While Rot Fungus Phanerochaete chrysosporium. Applied and Environmental Microbiology. 1995. Vol.61, N.11, p.3904-3909), but the bacteria of Pseudomonas genus are fastidious to nutrient medium and storage conditions. Fungi are less convenient in production, and they cause, among other things, a shift in the ecological equilibrium when employed in environment media.

SUMMARY OF THE INVENTION

It is an object of the invention to isolate a new strain of microorganisms, in particular, yeast, which is able to degrade higher PCB concentrations in environment media in situ under aerobic conditions, and which is convenient in production and employment.

The object of the invention is attained by providing a new, genetically resistant yeast strain of Hansenulla californica AT.

Hansenulla californica AT yeast strain has been isolated from soil and selected as the result of long-term subculturing of separate yeast colonies on a minimal salts medium (Practicum in Microbiology, M., MGU Publishers, 1976) containing

(NH₄)₂HPO₄ 1.5 g KH₂PO₄ 0.7 g NaCl 0.51 g Mg₂SO₄ 0.8 g distilled water up to 1 liter pH 7.2

in the presence of various PCB concentrations, from 100 to 400mg per a liter of a nutrient medium.

The yeast strain was selected by a PCB degradation level and velocity, and by its genetic PCB-resistance. Genetic resistance of selected strains was attained by repeated subculturing on dense nutrient media. Colonies grown on them were then subcultured on a minimal salts medium having the above composition.

As the result, a new genetically resistant yeast strain of Hansenulla californica AT has been obtained.

Identification of the microorganism was made in accordance with the Kreger-van Rij identifier. The strain, (identified as Hansenulla (Zygomilliopsis) californica AT), was deposited on Feb. 12, 1997, under the terms of the Budapest Treaty with the Russian National Collection of Industrial Microorganisms (Vserossiskaya kollektsiya promyshlennykh microorganismov, abbreviated as VKPM), and has the accession deposit number of VKPM Y-2284. The address of VKPM is: Russian National Collection of Industrial Microorganisms (VKPM), GNII genetika, Dorozhny proezd. 1, Moscow 113545, Russian Federation. The strain features the following culture, morphological, physiological and biochemical characters.

Culture and Morphological Characters:

The strain grows on a medium containing 5% malt extract. After incubation at 25° C. for 72 hours, a gram-stained smear contains slightly spherical cells of 2.4-6.2×3.0-8.1 μm in size. Colonies are white, opaque and circular. The yeast forms asci of zygotic origin on an acetate medium. In a liquid nutrient medium the growth takes place at a temperature of 29° C. during 72 hours at an agitator rotational speed of 500 rev/min.

Physiological Characters:

The strain is aerobic, grows at a temperature from +4° C., does not grow at a temperature of +42° C., the optimal temperature being +20° C. Grows at pH 5.0-7.5, optimal pH 6.8-7.0. Grows on rich nutrient media based on a meat infusion broth (MIB) and enzymic fish flour digest (EFFD).

Biochemical Characters:

In the Giss media, the strain assimilates saccharose, maltose, cellobiose, D-xylose, D-mannite, citric acid, lactic acid, alpha-methyl-d-glycoside as a sole carbon source. Ferments glucose for 3-5 days. Uses nitrogen of organic and inorganic origin.

Storage Media: EFFD or MIB and minimal salts media with PCB. To produce yeast biomass for degrading PCB, the strain may be incubated on various nutrient media containing common carbon and nitrogen sources, mineral salts. Carbon sources which can be used in the practice of the present invention are PCB, glucose, saccharose, maltose. A nitrogen source can be both organic and inorganic substances. Organic nitrogen sources can be EFFD, peptone, yeast autolysate, corn extract, etc. Inorganic nitrogen sources are ammonium salts.

Depending on the employed media composition and cultivation conditions, a culture liquid obtained can have a cell titer from 5.0*10⁶ to 1.0*10⁷ cells per cu cm.

The invention will be further explained by the following examples.

EXAMPLE 1 Production of Strain Biomass

Hansenulla californica AT yeast strain was incubated under aerobic conditions on a liquid MIB-based nutrient medium by a subsurface method at temperature t=29±2° C. and an agitator rotational speed of 200 rev/min for 72 hours. A titer of the incubated culture was 1.0*10⁷ cells per cu cm.

EXAMPLE 2 Soil Remediation Under Laboratory Conditions

Different PCB concentrations were introduced into a soil sample, followed by vigorous agitation of the sample

The obtained culture liquid was diluted with pipeline water up to a titer of 10⁶-10⁵-10⁴ cells per cu cm. The cell suspension was sprayed onto a surface of PCB-contaminated soil in the amount of a liter per sq. m. The soil was held at a room temperature for two months. Test samples were taken after 0.2, 1 and 2 months.

PCB concentration in the treated soil was determined on a “Crystal” gas-liquid chromatograph in accordance with a method disclosed in Methods for Determining Pesticide Microqualities in Food, Feedstuff and the Environment. T.2.M.—Agropromizdat.-1992, p.p. 143-148. PCB was extracted from the soil sample by hexane and introduced into the gas-liquid chromatograph equipped with an electron capture detector. Analysis results are summarized in Table 1.

Dynamics of PCB Degradation in Soil as a Function of Cell Concentration in a Suspension

TABLE 1 Cell concentration in suspension Time (cells per cu cm) (months) PCB concentration (mg/kg) 1 2 3 initial PCB concentration 32.6 49.0 70.2 10⁶ 0.5 20.3 17.6 42.8 1 15.2 15.1 30.3 2 8.5 7.7 18.9 10⁵ 0.5 22.1 17.9 54.8 1 11.6 10.3 29.4 2 20.7 34.8 28.3 10⁴ 0.5 28.5 28.1 55.7 1 15.3 7.6 41.0 2 10.4 10.2 42.9

As may be seen from Table 1, the most optimal cell concentration in a suspension to be introduced into soil is 10⁵ cells per cu cm, while a cell concentration of 10⁴ cells per cu cm appears ineffective.

A concentration of 10⁶ cells per cu cm in a suspension to be introduced into soil is unprofitable.

EXAMPLE 3 Soil Remediation in Situ

A cell suspension prepared as in Example 1 was sprayed onto a soil surface with the aid of a backpack sprayer in the amount of 1 liter per sq. m. Upon introduction of the suspension, the soil was carefully dug and hold at ambient temperature for 2 months. Test samples were taken after one and two months and analyzed as in the previous example.

Analysis results are presented in Table 2.

PCB Degradation in Situ

TABLE 2 second Test time Control first month month PCB content in soil 49.0 35.7 12.8 (mg/kg)

As will be seen from the data above, PCB concentration in soil samples was reduced by 45.3% within 2 months.

EXAMPLE 4 Water Decontamination

A cell suspension prepared as in Example 1 was added to 5 liters of sewage containing 25 mg/l PCB. The suspension was introduced in the amount of 10⁴ cells per liter. Upon introduction of the suspension, the water was continuously agitated at a speed of 10 rev/min during 14 days at a room temperature. Water samples were taken after one and two weeks and analyzed as in the previous example.

The analysis results are summarized in Table 3.

PCB Degradation in Water

TABLE 3 Test time control first week second week PCB content in water 25.0 15.6 5.1 (mg/kg)

As may be seen from the data above, PCB concentration in sewage was reduced by 49% after 2 weeks.

INDUSTRIAL APPLCABILITY

The yeast strain in accordance with the invention ensures approximately 50% reduction in PCB concentration in environment media. The strain is applicable to detoxicate environment media, in particular, soil, water and PCB-containing wastes of electrical and chemical industry.

In prospect, the strain may be employed to produce various organic compounds from PCBs and PCB-containing waste. 

What is claimed is:
 1. Hansenulla californica yeast strain VKPM Y-2284 for degrading polychlorinated biphenyls. 